Process of making paving compositions and products



JAMES EDGAR BLAGK AND MICHAEL A. POPKESS, OF KANSAS CITY, llTISfiOURI,

.KLE'SIGNOFJS T0 BITUMINIZED RGAD GQMEANY, OF KANSAS CITY, llIiZbSQUI-cll,

CGRPGEATION 91 ARIZONA.

P360335 01* B'XAKING PAVING COMPOSITIONS ANT! PROD'QCTS Lilli 142G72 v Specification of Letters Patent.

No Drawing.

T0 (ZZZ whom. it may concern:

DE 1b known that we, Janine EDGAR Brown and lvlrcninn Pornnss, citizens of the United States, and residents of Kansas City, in the county of Jackson and State of Missouri, have invented certain new and useful improvements Processes of" Making Paving Compositions and Products Thereof,

01 which the following is a specification.

or may be an asphaltic composition liquid at ordinary temperaturer, such impregna tiou being with the aid of vacuum and heat, impregnation being usually aided by pressure; and it further comprises as a new paving material a pulverulcnt relatively coarse grained limestone or the like having the grains thereof thoroughly in'ipregnated with bitumen. such bitumen filling all the natural pores with substantial completeness; all as more fully hereinafter set forth and as claimed.

Th oldest type of asphalt pavement was made with certain natural rocky or stony materials found in Europe and used originally in pa ing Paris. These natural materials consisted of particles of limestone and bitumen, the particles of the mineral matter being of extreme fineness and theroughly distributed through the bitumen. In material of the best quality, the proportion of bitumen and of limestone and their mutual relation were such that. the material Application filed April 18, 1917, Serial No. 162,509.

bitumen and some less;

ted Nov. 42,

Renewed September to, 1919. Serial in the bestsmnples there not quite enough asphalt or biturne' of this character there. should be about 13 per cent. to l! per cent. of asphalt while the average in this natural material rarely reaches 11 per cent. Much or? it goes low as 5 per cent.

in character, portions containing more and mixtures were, similarly, uneven. And the average content of asphalt was too little. In making; the

pavements the rocky material was heated,

crushed and ground and thoroughly mixed in order to obtain an average n'vaterial; but, as stated, the average material, even when of the best character, contained too little bitumen. sources were tried but did not ive l actory results for the reason that the for- I eign asphalt simply diluted the mixture and did not assume the same relation to the mineral matter as that of the original hitu- Various attemnts have been made to du- 86 "plicate this natural i'nate-rial but they have been uniformly unsuccess-iul for various reasons; and modern asphalt pavements in this country Where thisnatura-l material not available, are universally of entirely diifen ent types. They are built up structures containing aggregates of coarse mineral matter (sand with crushed rock or gravel) in interlocking engagement with the various portions of aggregate cemented by asphalt lay- 90 ers and with the voids filled with asphalt.

We have found that the lack of success in the various attempts at duplicating this natural paving material have been due to the fact that impregnation of the particles of limestone could not be made uniform. Any mechanically crushed limestone or like material is composed of grains of no great mechanical strength; the grains are porous-and are relatively friable. crushing with com 19 parative readiness. The pores are air-bound. In making a mixture of crushed.limestone with asphalt, it is diflicult to remove this air and cause the bitun'ien to enter the But if the pores are not entered by the as- 10 phalt and if the amount of asphalt chosen For a -navement 55 The natural. rock was uneven 60 Additions of asphalt froinet-her 70 that is the amount which will be, so to speak,

taken up by the, powder then in use whenthe particles of limestone crush further there is a production of unimpregnated' or uncoated grinding surfaces; The net result is that unless the pavement is made with enough asphalt to provide for subsequent impregna-' tion of the limestone particles as they are broken down under traffic, (in which case the pavement is soft and yielding because of this excess temporarily present), the whole pavement will disintegrate and form dusty or powdery material.

We have found that all these disadvantages may be obviated and a material produ'ced which, although like the natural Eu ropean material in that it consists mainly of asphalt and calcareous material and possessesthe stated advantages, is much more uniform in character and has the said advantage in a much higher degree. And itlias certain new advantages of its own. By this invention, it is possible to produce material of any desired relative ratio between calcareous material and bitumen; so that thereby a material may be produced having" the oplimum ratio of asphalt instead of ratio limited by the amount naturally present as in the case of native materials. In so doing, as we have found, it is only necessary to 'rely upon the simple expedient of performing the incorporation of asphalt and limestone dust under a vacuum. Operating under a vacuum, the air in the pores of the granules or grains is removed and the asphalt takes its place. Instead of the pores being airbound during the mlxing operation, and not being impregnated with bitumen, under the influence of the vacuum the air leaves and the bitumen takes its place. The operation should be. conducted with the materials hot as practicable to give a maximum of liquidity and penetration. Since the operation is under heat and vacuum, the asphalt should be as free as possible of oils 'volatilizing under the circumstances. For the sake of securing liquidity, We may mix the asphalt with more or less of an oil not volatilizing much at the temperature en'iploycd, perform my incorporation under vacuum and thereafter raise the whole mixture to a higher temperature, while still maintaining the vacuum, in order to remove these oils. Or we may indeed use some fluxing oil which is not volatile at all; or at 1' ast'i' ot to any substantial extent. We may use any-solid or semisolid asphalt, hat is any asphalt which is solid or semisolid under atmospheric conditions, though We find it often advantageous in many respects to use asphalts which are normally liquid at atmospheric temperatures. Since in the ultimate composition the amount of asphalt is always merely that which will sullice to impregnate without giving any free liqu d layers of substantial thickness, the liquid asphalts are here applicable as well as the solid varieties.

Under the present invention it is not necessary to grind the limestone to extreme fineness; there is not need oi striving to secure the extremely great subdivision of the calciun'i carbonate particlesthat exist in the stated European materials. it is sulficient to granulate it. \Vhatever the granule size, however, the material should be fairly uniform. The size of grain which is most advantageousv will depend to some extent upon the porosity of the limestone. With a soft highly porous material such as a shell marl or as a chalky limestone, rather coarse grains may be used, since the texture is open enough to permit intercommunicationof the pores and re1..:,)\'al of air throughout the enetiat1o1'1 of granules with simultaneous the asphalt throughout. omething of course also depends upon the coarseness or fineness of pore. As a generalrule, the harder the limestone, the finer we grind it; but in all cases it is, as compared with the mineral constituents existing in the natural asphalt rock, a relatively coarse material. A good material may be made even with the very hard limestones by grinding to less than 100 mesh, while with some softer limestones, a granule size of less than 20 mesh may be suflicient.

Any convenient type of mixing apparatus with means for incorporation under vacuum and heat may be used. With the small proportions of asphalt employed, the mixture is rather stiff, even. when quite hot and it is desirable that powerful disintegrating and stirring means be used. Ordinarily, we

work at about 180212 1 although we may use higher or lower temperatures, this depending largely upon the particular asphalt used. A proportion; of 11 per cent. to 19 per cent. asphalt in the finished product is desirable. The materials may be moist during incorporation with some advantage but the presence of the water vapor, unless work is at a low temperature, is inconvenient in malntaming the vacuum.

In a typical en'ibodiment of our invention we grind a limestone of ordinary hardnessto a fineness of less than 50 mesh; place this material in a rotatable drum provided with external heating means, create a vacuum of 15 to 25 inchesand introduce a suit-- able amount of normally liquid asphalt, or asphalt that has been liquefied by heating. Steam is then introduced which furnishes pressure to cause impregnation of the pores of the limestone by the asphalt and also serves to retain the asphalt in a liquid con-.

dition. The proportion of this asphalt may be 11 to 19 per cent. of the final product.

neating and mixing are continued until the air is sutiiciently removed from the. pores and the liqmd asphalt has disappeared and the impregnation of the particles is complete. \Vith the liquid asphalt the temperaturemay be around 200 .F. Heat in using a liquid asphalt is onlydesirable as shortening the period of treatment. With asphalts which are solid or semisolid at ordinary temperatures. heat is necessary to produce liquidity either before or during the mixin At the end of the incorporation the drum will contain a more or less ulverulent black mass of impregnated limestone grains. This material may be kept and stored indefinitely. In use we heat it somewhat and deposit it on the roadway; thereafter rolliugit or tamping it in place. \Ve may press it into blocks, and use these. \Vhileihe. material is substantially dry in the sense that it will not give up any substantial amount of asphalt to other materials. yetthere is enough tihn coating on the faces of the grains to make them adhere when they are pressed together. The pavement made by the material is permanent. hard, dense malleable and resistant to all the stresses and strains of tratlic. not disintegrating. softening. rutting or waving. But it is malleable enough to make repair easy. Under pressure. it can be given any contour or shape desirable.-

lVhat we claim is:

r 1. The process of making a paving material which comprises disintegrating a natural calcareous material and mixing the resultant material with a binder having adhesive and waterproof qualities under a substantial.vacuum. the quantity of hinder used calcareous material. 2. The process of makinga paving material which comprises crushing a natural calcareous material and mixing the resultant material with asphalt under vacuum and being just. sutlieientto till the pores of ltllG heat, the quantity of binder used being just sutlicient. to fill the pores of the calcareous material.

3. The process of making a paving material which comprises disintegrating a natural calcareous material and mixing the resultantmaterial with a binder having adhesive and waterproof qualities under vacu-.

um, the quantity of binder usedbeing just sufiicient to fill the pores of the calcareous material.

l. The process of making a paving material which comprises pulverizing a natural calcareous material and mixing the resultant material with from 11 to '19 per cent. of normally liquid asphalt under vacuum and. heat.

5. The process of making a paving material which comprises eomminuting limestone and mixing the resultant material under vacuum with the proper proportlon of as phalt to make it non-flowing, malleable and tratlic supporting.

(3. The process of making a paving material which comprises disintegrating limestone and mixing the resultant material.

under acuiun and heat with the proper In testimony whereof we atlii; our signatures hereto.

JAMES EDGAR BLACK. MICHAEL A. POPKESS. 

